Generally, modulator and photodetector devices that use surface plasmon polariton (SPP) modes can be classified along two distinct architectures. The first architecture can be based on the phenomenon of attenuated total reflection (ATR) and the second architecture can be based on the propagation of surface plasmon polaritons (SPPs) along an appropriate waveguide.
ATR-based devices generally include coupling of an out-of-plane optical beam to SPPs propagating on a metal surface, such as with the aid of a prism or a grating. At a specific angle of incidence, which can depend on one or more of the optical wavelength, the materials used, and the particular geometry of the device, coupling to SPPs can be enhanced (e.g., maximized) and a drop in the power reflected from the metal surface can be observed. ATR-based modulators can make use of this attenuated reflection phenomenon. For example, at least one of the optical parameters of one of the dielectrics or semiconductors bounding the metal structure can be varied (e.g., electrically or otherwise), such as to shift the angle of incidence where enhanced (e.g., maximized) coupling to SPPs occurs. In an illustrative example, electrically shifting the angle of maximum coupling can modulate the intensity of reflected light. See, for example, U.S. Pat. Nos. 5,625,729; 5,155,617; 5,157,541; 5,075,796; 4,971,426; 4,948,225; 4,915,482; 4,451,123; 4,432,614; and 4,249,796, the contents of each of which are hereby incorporated herein by reference.
ATR-based photodetectors can make use of attenuated reflection phenomenon along with detecting a photocurrent generated in the structure via Schottky barrier photo-emission or through the generation of electron-hole pairs in a semiconductor bounding the metal structure. In one approach, ATR-based modulators or photodetectors can be implemented using a prism to couple the incident optical beam to SPPs. However, such configurations are generally bulky and not suitable to mass-manufacturing. In another approach, ATR-based modulators or photodetectors can be implemented using a grating to couple the incident optical beam to SPPs. However, such a grating configuration generally does not provide suitable performance (e.g., electrical or optical), such as would require impractical drive voltages or drive currents, or having large insertion loss, low modulation depth or responsivity, or requiring materials that are not yet available for mass-manufacturing.
In other examples, modulators and photodetectors can be implemented using surface plasmon waveguides. For example, metal stripe long-range surface plasmon waveguides and integrated passive elements such as splitters, Mach-Zehnder interferometers, couplers and Bragg gratings can be implemented. See, for example, U.S. Pat. Nos. 6,442,321; 6,914,999; 6,801,691; 6,741,782; 6,823,111; and 7,151,789. Such structures can be used to implement modulators. See, for example, U.S. Pat. Nos. 6,914,999 and 7,043,134. Also see, for example, U.S. Pat. No. 7,026,701 including a photodetector. Short-range surface plasmon waveguides comprising metal claddings can be used to implement modulators based on silicon and indium tin oxide. Such waveguide-based modulators and photodetectors are generally suitable for end-fire excitation (e.g., butt-coupling), but are generally not well suited to surface (e.g., broadside) excitation.
U.S. Pat. No. 7,109,739 mentions optical components and an apparatus for testing silicon on insulator (SOI) wafers bearing mixed integrated optoelectronic and electronic circuits; the optical components include a dielectric prism or grating coupler designed to excite SOI waveguides, and the electrical test points are formed conventionally as metallic contact pads. U.S. Pat. No. 7,262,852 mentions a method for testing wafers bearing integrated optical or optoelectronic circuits, based on aligning an input beam to various alignment features and couplers defined on a wafer.
In one approach for optical non-contact testing of silicon electronic wafers, silicon photodiodes are used for receiving optical data on-wafer at photon energies above the bandgap of silicon, and avalanche diodes were used as light emitting diodes emitting visible light for sending optical data off wafer. However, such an approach can have disadvantages, because it is susceptible to cross-talk, the optical output power emitted by the light emitting diode is very weak, and large voltages are required to drive the emission.